The present invention relates to apparatus forming a service channel in a radio system in which the service channel carrier lies at the lower frequency end of the radio system base band.
Service channel systems are aids in communication which extend parallel to the main radio transmission path. They permit service conversations for maintaining operation between radio stations and their relay stations. In order to make communications over the service channel as secure as possible, it is known to exclude all operating devices from the transmission and to modulate the service channel signal directly onto the emitted radio signal. Such a process is very complicated since extensive additional devices are required and mainly also because this service channel is intended to be used not only for telephone conversations but also for the transmission of indication signals regarding operating states, switching signals to standby devices, and measured value signals as well.